The Case of the Vanished Variable – A Ruby Mystery Story

After a stressful couple of days at work, Deirdre Bug is looking forward to a quiet evening in. But her plans are thwarted when the phone rings. “I know I’m the last person you want to hear from…but...I need your help!” Follow Deirdre as she embarks on an adventure that features a looming Demo Day with serious prize money up for grabs, a trip inside the walls of one of the Ruby community’s most revered institutions, and some broken code that appears to be much more simple than meets the eye.

Transcript

1. THE CASE OF THE VANISHED VARIABLE A Ruby Mystery Story Nadia Odunayo, @nodunayo
9. 3 million unique visitors per month
10. 36 million pageviews per month
11. 110 million requests per month
17. 👀
19. 🕵
23. 💰💰💰
24. 💰💰💰
25. Nadia Odunayo
26. Nadia Odunayo
27. Deirdre Bug
28. Deirdre Bug
29. Dee Bug
30. CASE FILES
31. CASE FILES #048
32. CASE FILES #048 Vanished Variable
33. CHAPTER ONE
42. 📞
43. 📞
44. I know I’m the last person you want to hear from…
45. …but I need your help!
46. …but I need your help! 👱
47. Jenny • 29 years old 👱
48. Jenny • 29 years old • Ruby developer 👱
49. Jenny • 29 years old • Ruby developer • Rails obsessed 👱
50. Jenny • 29 years old • Ruby developer • Rails obsessed 👱 • Betrayed her best friend
51. Ruby Institute of Professionals
52. RIP Ruby Institute of Professionals
53. Incubator RIP
54. Incubator • Help Ruby’s image RIP
55. Incubator • Help Ruby’s image • Startup ideas RIP
56. Incubator • Help Ruby’s image • Startup ideas • $500k prize RIP
57. Incubator • Help Ruby’s image • Startup ideas • $500k prize • Jenny’s team in fi nal two RIP
58. We’re building a platform that assigns grants… 👱
59. There are three different types of award… 👱
60. Our demo simulates an example draw… 👱
61. …but our code has a bug! 👱
62. It’s so close between the fi nal two teams… 👱
63. 🧔
64. 😰 🧔
65. We need you. 👱
68. 🕵
69. 💰💰💰
70. 💰💰💰
72. CHAPTER TWO
73. I don’t need help. 🧔
74. But, Alex…! 👱
76. I’ll tell you what, Alex… 🕵
79. …you’ll fi nd the bug quicker! 🕵
80. Fine. 🧔
81. 👱
82. 💪 👱
83. There’s con fi dential code in here! 🧔
87. 40 minutes later…
88. class AwardA < Grant @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_a.rb
89. class AwardA < Grant @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_a.rb
90. class AwardA < Grant @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_a.rb
91. class AwardA < Grant @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_a.rb
92. class AwardA < Grant @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_a.rb
93. class AwardA < Grant @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_a.rb
94. class AwardA < Grant @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_a.rb
95. @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_a.rb class AwardA < Grant
96. @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_b.rb
97. @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_b.rb class AwardB < Grant
98. @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_c.rb
99. @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_c.rb class AwardC < Grant
100. class Grant
 MAX_GRANTS = 100 @award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
101. class Grant
 MAX_GRANTS = 100 @award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
102. class Grant
 MAX_GRANTS = 100 @award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
103. class Grant
 MAX_GRANTS = 100 @award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
104. class Grant
 MAX_GRANTS = 100 @award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
105. class Grant
 MAX_GRANTS = 100 @award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
106. class Grant
 MAX_GRANTS = 100 @award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
107. 50.times do AwardA.assign! end assign_a.rb
108. 30.times do AwardB.assign! end assign_b.rb
109. 20.times do AwardC.assign! end assign_c.rb
110. puts Grant.award_count puts Grant.awards_remaining Grant.assign_remaining! redraw.rb
111. puts Grant.award_count puts Grant.awards_remaining Grant.assign_remaining! redraw.rb
112. class Grant
 MAX_GRANTS = 100 @award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
113. 50.times do AwardA.assign! end
114. 50.times do AwardA.assign! end
115. 50.times do AwardA.assign! end 30.times do AwardB.assign! end +
116. 50.times do AwardA.assign! end 30.times do AwardB.assign! end +
117. 50.times do AwardA.assign! end 30.times do AwardB.assign! end + 20.times do AwardC.assign! end +
118. 50.times do AwardA.assign! end 30.times do AwardB.assign! end + 20.times do AwardC.assign! end +
119. 50.times do AwardA.assign! end 30.times do AwardB.assign! end + 20.times do AwardC.assign! end + =
120. 50.times do AwardA.assign! end 30.times do AwardB.assign! end + 20.times do AwardC.assign! end + = 100
121. 50.times do AwardA.assign! end 30.times do AwardB.assign! end + 20.times do AwardC.assign! end + = 100 =
122. 50.times do AwardA.assign! end 30.times do AwardB.assign! end + 20.times do AwardC.assign! end + = 100 = MAX_GRANTS
123. Following so far…? 🧔
124. I got it. 🕵
125. alex:rip_grant_program/ $
126. alex:rip_grant_program/ $ ruby grant_awards.rb Awarding 50 grants of type A… Awarding 30 grants of type B… Awarding 20 grants of type C… Checking if prize redraw is needed… Total number of grants awarded so far… 300 Awards left to assign: -200 ERROR: Maximum number of grants exceeded!
127. alex:rip_grant_program/ $ ruby grant_awards.rb Awarding 50 grants of type A… Awarding 30 grants of type B… Awarding 20 grants of type C… Checking if prize redraw is needed… Total number of grants awarded so far… 300 Awards left to assign: -200 ERROR: Maximum number of grants exceeded!
129. CHAPTER THREE
130. 🕵
131. @award_count
132. class AwardA < Grant @award_count = 0 … end
133. class AwardA < Grant @award_count = 0 … end class AwardB < Grant @award_count = 0 … end
134. class AwardA < Grant @award_count = 0 … end class AwardB < Grant @award_count = 0 … end class AwardC < Grant @award_count = 0 … end
135. class AwardA < Grant @award_count = 0 … end class AwardB < Grant @award_count = 0 … end class AwardC < Grant @award_count = 0 … end class Grant
 MAX_GRANTS = 100 @award_count = 0 … end
136. What if each class were to have a differently-named class instance variable? 🕵
137. Sure…we can try that. 🧔
138. class AwardA < Grant @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_a.rb
139. class AwardA < Grant @award_a_count = 0 def self.award_count @award_a_count end
 
 def self.assign! @award_a_count += 1 end end award_a.rb
140. class AwardA < Grant @award_a_count = 0 def self.award_count @award_a_count end
 
 def self.assign! @award_a_count += 1 end end award_a.rb
141. alex:rip_grant_program/ $
142. alex:rip_grant_program/ $ ruby grant_awards.rb Awarding 50 grants of type A… Awarding 30 grants of type B… Awarding 20 grants of type C… Checking if prize redraw is needed… Total number of grants awarded so far… 300 Awards left to assign: -200 ERROR: Maximum number of grants exceeded!
145. Alex! You’ll never guess who’s in the of fi ce! 🧑🦱
146. Matz! 🧑🦱
148. 🏃💨
149. 🏃💨
150. 🏃💨
151. 🏃💨 💰💰💰 💰💰💰 💰💰💰
152. ⌨
153. 🕵
154. $
155. $ git status
156. $
157. $ git diff
159. +++ b/assign_c.rb @@ -0,0 +1,151 @@
160. +++ b/assign_c.rb @@ -0,0 +1,151 @@
161. 20.times do AwardC.assign! end assign_c.rb
163. class Grant @award_count = 300 def self.award_count @award_count end end
164. What are you looking at? 🧔
165. Where did you get my old code from? 🧔
166. That’s from an old demo. 🧔
167. It was at the bottom of this fi le… 🕵
168. 🧔
169. 😳 🧔
170. …you never do partial commits? 🕵
171. 🧔
172. 😳 🧔
173. 🕵
174. 😌 🕵
175. c c c c c G G G G G @ @ @ @ @ @ @ @ @ @ @ @ = d d d s s s s .a a a a a a a a a a a @ @ @ @ @ @ @ @ @ @ @ @ e e e e e e
177. alex:rip_grant_program/ $
178. alex:rip_grant_program/ $ ruby grant_awards.rb Awarding 50 grants of type A… Awarding 30 grants of type B… Awarding 20 grants of type C… Checking if prize redraw is needed… Total number of grants awarded so far… 100 Awards left to assign: 0 SUCCESS: All awards assigned!
180. CHAPTER FOUR
181. Dee!! 👱
182. I’m not the “told- you-so” type, but… 👱
183. ….I knew him using class variables was a bad idea! 👱
184. 🕵 You mean class instance variables!
185. 🕵 You mean class instance variables! 👱 No, class variables!
186. 🕵 You mean class instance variables! 👱 No, class variables! 🕵 You don’t mean class instance variables?
187. @@award_count
188. @award_count
189. 👱
190. 🤨 👱
191. Do you have time to come back upstairs? 👱
192. What? There’s nothing con fi dential in here! 👱
193. 🕵
194. 🤨 🕵
195. 🕵 😲
196. class AwardA < Grant @award_count = 0 def self.award_count @award_count end
 
 def self.assign! @award_count += 1 end end award_a.rb
197. class AwardA < Grant @@award_count = 0 def self.award_count @@award_count end
 
 def self.assign! @@award_count += 1 end end award_a.rb
198. class Grant
 MAX_GRANTS = 100 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
199. Let’s run the code! 🕵
200. jenny:rip_grant_program/ $
201. jenny:rip_grant_program/ $ ruby grant_awards.rb Awarding 50 grants of type A… Awarding 30 grants of type B… Awarding 20 grants of type C… Checking if prize redraw is needed… Total number of grants awarded so far… 100 Awards left to assign: 0 SUCCESS: All awards assigned!
202. Hey…check this out… 🕵
204. class Grant
 MAX_GRANTS = 100 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
205. class Grant
 MAX_GRANTS = 100 @@award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
206. class Grant
 MAX_GRANTS = 100 @@award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
207. Let’s run this code! 🕵
208. jenny:rip_grant_program/ $
209. jenny:rip_grant_program/ $ ruby grant_awards.rb Awarding 50 grants of type A… Awarding 30 grants of type B… Awarding 20 grants of type C… Checking if prize redraw is needed… Total number of grants awarded so far… 300 Awards left to assign: -200 ERROR: Maximum number of grants exceeded!
211. Let’s go and fi nd Alex! 👱
212. He was trying to fi nd a quiet corner to take a personal call. 🧑🦱
213. Zoë, they almost caught me... 🧔
214. …even brought in a private investigator… 🧔
215. …faked some code for fun and to buy time… 🧔
216. …Jenny will be nosy so I fi xed the real code for now… 🧔
217. But don’t worry, honey… 🧔
218. …I’ll put the bug back in before the fi nal tomorrow! 🧔
219. 🧔
220. 😰 🧔
221. CHAPTER FIVE
222. So… 🕵
223. 🧔
224. 🧔💘
225. 👩🦱 🧔💘
226. 👩🦱 Zoë’s team
227. 👩🦱 Zoë’s team vs 👱 Jenny’s team
228. 👩🦱 Zoë’s team vs 👱 Jenny’s team for
229. 👩🦱 Zoë’s team vs 👱 Jenny’s team for 💰💰💰
230. 🧔
231. 🧔 My team’s idea = 😴
232. 🧔 Zoë’s team’s idea = 😍
233. 🧔 Zoë’s team’s idea = My idea! 😌
234. 👩🦱 Zoë’s team vs 👱 Jenny’s team
235. 👩🦱 Zoë’s team vs 👱 Jenny’s team 🥇 🥈
236. 👩🦱 🧔💘
237. 🧔
238. 😼 🧔
239. class AwardA < Grant @@award_count = 0 def self.award_count @@award_count end
 
 def self.assign! @@award_count += 1 end end
240. class AwardA < Grant @@award_count = 0 def self.award_count @@award_count end
 
 def self.assign! @@award_count += 1 end end
241. class AwardA < Grant @@award_count = 0 def self.award_count @@award_count end
 
 def self.assign! @@award_count += 1 end end 🕵
242. class AwardA < Grant @@award_count = 0 def self.award_count @@award_count end
 
 def self.assign! @@award_count += 1 end end Those class variables look suspect… 🕵
243. …faked some code for fun and to buy time… 🧔
244. ⌛
246. Yup. 👱
247. Wow. 🕵
249. deebug:vanished_variable/ $
250. deebug:vanished_variable/ $ pry [1] pry(main)> class Grant [1] pry(main)* @@type = “Grant” [1] pry(main)* def self.type [1] pry(main)* @@type [1] pry(main)* end end [1] pry(main)* => :type [2] pry(main)> Grant.type => “Grant”
251. [2] pry(main)> Grant.type => “Grant”
252. [2] pry(main)> Grant.type => “Grant” [3] pry(main)> class AwardA < Grant [3] pry(main)* @@type = “A” [3] pry(main)* def self.type [3] pry(main)* @@type [3] pry(main)* end end [3] pry(main)* => :type [4] pry(main)>
253. [3] pry(main)* def self.type [3] pry(main)* @@type [3] pry(main)* end end [3] pry(main)* => :type [4] pry(main)>
254. [3] pry(main)* def self.type [3] pry(main)* @@type [3] pry(main)* end end [3] pry(main)* => :type [5] pry(main)> Grant.type => “A” [4] pry(main)> AwardA.type => “A”
255. class Grant @type = “Grant”
256. class Grant class AwardA @type = “Grant” @type = “A”
257. class Grant class AwardA @type = “Grant” @type = “A” inherits from
258. @@type = “Grant” class Grant
259. @@type = “Grant” @@type = “A” class Grant class AwardA
260. @@type = “A” @@type = “A” class Grant class AwardA inherits from
261. Does direction matter? 🕵
262. [6] pry(main)>
263. [6] pry(main)> [7] pry(main)> Grant.superclass => Object [8] pry(main)> class Object [8] pry(main)* @@type = “Object” [8] pry(main)* def self.type [8] pry(main)* @@type [8] pry(main)* end end [8] pry(main)* => :type
264. [8] pry(main)* def self.type [8] pry(main)* @@type [8] pry(main)* end end [8] pry(main)* => :type [9] pry(main)>
265. [8] pry(main)* def self.type [8] pry(main)* @@type [8] pry(main)* end end [8] pry(main)* => :type [10] pry(main)> [9] pry(main)> Object.type => “Object”
266. [8] pry(main)* def self.type [8] pry(main)* @@type [8] pry(main)* end end [8] pry(main)* => :type [10] pry(main)> Grant.type [9] pry(main)> Object.type => “Object” RuntimeError: class variable @@type of Grant is overtaken by Object from (pry):4:in `type' [11] pry(main)>
267. [10] pry(main)> Grant.type [9] pry(main)> Object.type => “Object” RuntimeError: class variable @@type of Grant is overtaken by Object from (pry):4:in `type' [11] pry(main)>
268. [10] pry(main)> Grant.type [9] pry(main)> Object.type => “Object” RuntimeError: class variable @@type of Grant is overtaken by Object from (pry):4:in `type' [11] pry(main)> AwardA.type RuntimeError: class variable @@type of Grant is overtaken by Object from (pry):11:in `type' [12] pry(main)>
269. @@type = “A” @@type = “A” class Grant class AwardA inherits from
270. @@type = “A” @@type = “A” class Grant class AwardA inherits from inherits from class Object
271. @@type = “A” @@type = “A” class Grant class AwardA inherits from inherits from class Object @@type = “Object”
272. class Grant class AwardA inherits from inherits from class Object @@type = “Object” @@type = RuntimeError @@type = RuntimeError
273. I wonder how far up the inheritance chain this goes! 🕵
274. [12] pry(main)>
275. [12] pry(main)> [13] pry(main)> Grant.ancestors => [Grant, Object, PP::ObjectMixin, Kernel, BasicObject] [14] pry(main)> class BasicObject [14] pry(main)* @@type = “Basic” [14] pry(main)* def self.type [14] pry(main)* @@type [14] pry(main)* end end [14] pry(main)* => :type [15] pry(main)>
276. [14] pry(main)> class BasicObject [14] pry(main)* @@type = “Basic” [14] pry(main)* def self.type [14] pry(main)* @@type [14] pry(main)* end end [14] pry(main)* => :type [15] pry(main)>
277. [14] pry(main)> class BasicObject [14] pry(main)* @@type = “Basic” [14] pry(main)* def self.type [14] pry(main)* @@type [14] pry(main)* end end [14] pry(main)* => :type [15] pry(main)> Grant.type RuntimeError: class variable @@type of Grant is overtaken by BasicObject from (pry):4:in `type' [16] pry(main)>
278. Time for some good ol’ pen and paper! 🕵
279. RClass
280. RClass Class instance variables @type
281. RClass Class instance variables @type Class variables @@type
282. RClass Class variables @@award_count = 0 : Grant
283. RClass Class variables @@award_count = 0 : Grant RClass: AwardB RClass: AwardA RClass: AwardC
284. RClass Class variables @@award_count = 0 : Grant RClass: AwardB RClass: AwardA RClass: AwardC class AwardA < Grant @@award_count = 0 … end
285. 50.times do AwardA.assign! end assign_a.rb
286. class AwardA < Grant @@award_count = 0 def self.award_count @@award_count end
 
 def self.assign! @@award_count += 1 end end award_a.rb
287. RClass Class variables @@award_count = 0 : Grant RClass: AwardB RClass: AwardA RClass: AwardC 50.times do AwardA.assign! end
288. RClass Class variables @@award_count = 50 : Grant RClass: AwardB RClass: AwardA RClass: AwardC 50.times do AwardA.assign! end
289. RClass Class variables @@award_count = 50 : Grant RClass: AwardB RClass: AwardA RClass: AwardC 50.times do AwardA.assign! end
290. class AwardA < Grant @@award_count = 0 def self.award_count @@award_count end
 
 def self.assign! @@award_count += 1 end end award_a.rb
291. RClass Class variables @@award_count = 50 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 50
292. RClass Class variables @@award_count = 50 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 50
293. RClass Class variables @@award_count = 50 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 50 AwardB.award_count = 50 AwardC.award_count = 50
294. RClass Class variables @@award_count = 50 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 50 AwardB.award_count = 50 AwardC.award_count = 50
295. RClass Class variables @@award_count = 50 : Grant RClass: AwardB RClass: AwardA RClass: AwardC 30.times do AwardB.assign! end
296. RClass Class variables @@award_count = 80 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 80 AwardB.award_count = 80 AwardC.award_count = 80
297. RClass Class variables @@award_count = 80 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 80 AwardB.award_count = 80 AwardC.award_count = 80
298. RClass Class variables @@award_count = 80 : Grant RClass: AwardB RClass: AwardA RClass: AwardC 20.times do AwardC.assign! end
299. RClass Class variables @@award_count = 100 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 100 AwardB.award_count = 100 AwardC.award_count = 100
300. RClass Class variables @@award_count = 100 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 100 AwardB.award_count = 100 AwardC.award_count = 100
301. class Grant
 MAX_GRANTS = 100 @@award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
302. class Grant
 MAX_GRANTS = 100 @@award_count = 0 def self.award_count AwardA.award_count +
 AwardB.award_count +
 AwardC.award_count end
 
 def self.awards_remaining MAX_GRANTS - self.award_count end end grant.rb
303. RClass Class variables @@award_count = 100 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 100 AwardB.award_count = 100 AwardC.award_count = 100
304. RClass Class variables @@award_count = 100 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 100 AwardB.award_count = 100 AwardC.award_count = 100
305. alex:rip_grant_program/ $ ruby grant_awards.rb Awarding 50 grants of type A… Awarding 30 grants of type B… Awarding 20 grants of type C… Checking if prize redraw is needed…
306. alex:rip_grant_program/ $ ruby grant_awards.rb Awarding 50 grants of type A… Awarding 30 grants of type B… Awarding 20 grants of type C… Checking if prize redraw is needed… Total number of grants awarded so far… 300 Awards left to assign: -200 ERROR: Maximum number of grants exceeded!
307. 🕵
308. 😌 🕵
309. I know just the person! 🕵
310. CHAPTER SIX
311. 👳
312. 👳 Ellen • 45 years old
313. 👳 Ellen • 45 years old • Freelance developer
314. 👳 Ellen • 45 years old • Freelance developer • Ruby committer
315. RClass Class variables @@award_count = 100 : Grant RClass: AwardB RClass: AwardA RClass: AwardC AwardA.award_count = 100 AwardB.award_count = 100 AwardC.award_count = 100
316. 🕵 Did I get it right??
317. 👳 Yes! Except for one small thing…
318. RClass Class instance variables @type Class variables @@type
319. RClass
320. RClass
321. RClass Class-level variables @type @@type
322. 🕵 Class variables only seem to cause a lot of trouble…
323. 👳 Application con fi guration!
325. 🕵 But does the everyday developer have to care about them?
326. 👳 Well…let me tell you a story…
327. [14] pry(main)> class BasicObject [14] pry(main)* @@type = “Basic” [14] pry(main)* def self.type [14] pry(main)* @@type [14] pry(main)* end end [14] pry(main)* => :type [15] pry(main)>
328. [14] pry(main)> class BasicObject [14] pry(main)* @@type = “Basic” [14] pry(main)* def self.type [14] pry(main)* @@type [14] pry(main)* end end [14] pry(main)* => :type [15] pry(main)> Grant.type RuntimeError: class variable @@type of Grant is overtaken by BasicObject from (pry):4:in `type' [16] pry(main)>
330. Eileen M. Uchitelle @eileencodes
331. Aaron Patterson @tenderlove Eileen M. Uchitelle @eileencodes
332. RClass Class variables @@award_count = 0 : Grant RClass: AwardB RClass: AwardA RClass: AwardC
337. We should build a cache! We should build a cache!
339. Grant AwardA AwardA.award_count @@award_count
340. Grant AwardA AwardA.award_count @@award_count ActiveSupport Object PP::ObjectM @@award_count? @@award_count? @@award_co
341. AwardA.award_count Grant AwardA @@award_count ActiveSupport Object PP::ObjectM @@award_count? @@award_count? @@award_co
342. AwardA.award_count pport Object PP::ObjectMixin count? @@award_count? @@award_count?
343. AwardA.award_count pport Object PP::ObjectMixin count? @@award_count? @@award_count? Kernel @@award_count?
344. AwardA.award_count pport Object PP::ObjectMixin count? @@award_count? @@award_count? Kernel BasicObject @@award_count? @@award_count?
345. Grant AwardA AwardA.award_count @@award_count ActiveSupport Object PP::ObjectM
346. Grant AwardA AwardA.award_count @@award_count ActiveSupport Object PP::ObjectM CACHE
347. Grant AwardA AwardA.award_count @@award_count ActiveSupport Object PP::ObjectM @@award_count? @@award_count? @@award_co CACHE Grant
351. 👳 Why did I tell you this story?
352. Ruby is slow! 🧑🦳
353. Ruby is slow! 🧑🦳 Ruby doesn’t scale! 🧑🌾
354. Ruby is slow! 🧑🦳 Ruby doesn’t scale! 🧑🌾 Ruby is dying! 👩🔧
357. Learn Ruby
358. Understand Ruby
359. Improve Ruby
360. Ruby is slow! 🧑🦳 Ruby doesn’t scale! 🧑🌾 Ruby is dying! 👩🔧
362. Keep Ruby alive
363. 🕵
364. 🤩 🕵
365. EPILOGUE
367. Alex was fi red from the RIP…
369. The RIP Grant Program won the $500k prize and continues to run successfully, headed up by Jenny…
371. The shady mastermind behind Ruby is still at large…
372. THE END
373. THE END?